Probably the most often made customization of the mail database is to put a corporate logo into the letterhead. So why not allow an admin to do this without having to fiddle with the design?
Instead there could be a policy option to provide the logo.
My suggestion is this: replace the Notes memo letterhead with a photo of the sender.
This could be achieved by modifying the mailfile template to display an image called from a Directory view. This might use a new index value or simply use the person's internal name.
If integrated ...
My partner works for the same company I do and she went recently on maternity leave. I was a bit curious what she wrote in her out of office message.
When I sent her an short message to check the response I only got returned a flat text message.
Then this idea ...